American Viticultural Areas (AVAs) are wine grape-growing regions designated by the U.S. Alcohol and Tobacco Tax and Trade Bureau (TTB).  According to the TTB, the boundaries of an AVA should enclose a region that has features related to climate, geology, soils, and physical geography that affect viticulture in ways that are distinctive relative to areas outside of the boundaries. Based on these criteria, it could be assumed that AVAs are based primarily on unique terroirs. However, the TTB has permitted AVAs to define their boundaries utilizing highways, utility lines, irrigation ditches and other cultural features that in most cases do not correspond with the limits of the physical characteristics (e.g. soil series boundaries, geologic contacts) that define terroir. Also many, if not most AVAs are relatively large areas that encompass dramatic variations in soils, geology, and climate. AVAs are therefore not actually terroir-based, but instead represent collections of terroirs assembled for the purposes of marketing the wines of a particular region. An opportunity to counter this model was recently afforded by the owners of vineyards located in the alluvial fan of the Walla Walla River, an area that has produced some of the most critically acclaimed wines in North America. The petition drafted at the request of these viticulturalists utilized topographic, geologic, and soil maps to define an AVA that is remarkably homogenous with respect to geomorphology, geology, and soils. Encompassing 1524 hectares (3767 acres), the area within the boundaries of the "Rocks District of Milton-Freewater" AVA lies entirely on one landform (the Walla Walla River alluvial fan), has Quaternary alluvium as it's only geologic unit, and a single soil series (the Freewater), comprises 96% of its soils. The creation of boundaries that correspond precisely to the limits of essential terroir-defining characteristics is impeded by TTB requirements, which restrict petitioners to boundary lines derived from features that appear on USGS topographic maps. Sinuous boundaries such as those between contrasting soil series or geologic units cannot be utilized to define AVAs and must be approximated by straight-line segments.